Presentation on theme: "Data Center Networking with Multipath TCP"— Presentation transcript:
1 Data Center Networking with Multipath TCP UCLData Center Networking with Multipath TCPCostin RaiciuUniversity College London & Universitatea Politehnica BucurestiChristopher Pluntke, UCLAdam Greenhalgh, UCLSebastien Barre, Universite Catholique LouvainDamon Wischik. UCLMark Handley, UCL
2 Data Center Networking Today Resource AllocationTCPPath SelectionRandom load balancingRoutingOSPF, VLANs, TRILLShow multiple paths between serversSay that network is rearrangeably non blockingClosTopologyFatTree, VL2, BCube,multi-rooted tree2
3 Data Center Networking Tomorrow Resource AllocationMultipathTCPTCPPath SelectionRandom load balancingRoutingOSPF, VLANs, TRILLShow multiple paths between serversSay that network is rearrangeably non blockingClosTopologyFatTree, VL2, BCube,multi-rooted tree3
4 Data Centers are Important Cloud computingEconomies of scale: networks of tens of thousands of hostsCool appsWeb search, GFS, BigTable, DryadLINQ, MapReduceDense traffic patterns
5 Flexibility is Important in Data Centers Apps distributed across thousands of machines.Flexibility: want any machine to be able to play any role.But:Traditional data center topologies are tree based.Don’t cope well with non-local traffic patterns.Many recent proposals for better topologies.
6 Traditional Data Center Topology Core Switch10GbpsAggregation Switches10GbpsTop of RackSwitches1GbpsRacks ofservers…
7 Fat Tree Topology [Fares et al., 2008; Clos, 1953] K=4Aggregation Switches1GbpsK Pods withK Switcheseach1GbpsShow multiple paths between serversSay that network is rearrangeably non blockingClosRacks ofservers7
10 How Do We Use this Capacity? Need to distribute flows across paths.Basic solution: Random Load Balancing.Use Equal-Cost Multipath (ECMP) routing.Hash to a path at random.Use many differently rooted VLANs.End-host hashes to a VLAN; determines path.
11 Collisions Racks of servers 1Gbps 1Gbps Show multiple paths between serversSay that network is rearrangeably non blockingClosRacks ofservers11
12 Can MPTCP self-optimize data-center traffic? With Multipath TCP we can explore many paths:Instead of using one random path, use many random pathsDon’t worry about collisions.Just don’t send (much) traffic on colliding paths
13 Simulation Setup~8000 hostsLong-lived flowsPermutation traffic matrixEach hosts sends and receives from a single other randomly chosen hostSmallest amount of traffic that can fill the network
14 Multipath TCP in the Fat Tree Topology Throughput Allocation
16 Overloaded Fat Tree: better fairness with Multipath TCP
17 Centralized Scheduling With RLB, it’s really hard to utilize FatTree.Hedera [Fares et al.,2010] uses a centralized scheduler and flow switching.Start by using RLBMeasure all flow throughput periodically.Any flow using more than 10% of its interface rate is explicitly scheduled onto an unloaded link.How does centralized scheduling compare with MPTCP?
18 MPTCP vs Centralized Dynamic Scheduling Centralized Scheduling MPTCPAnimate tough part of the graphInfiniteScheduling Interval18
19 Can’t we just use many TCP connections? Loss rate of MP-TCP (“linked”) vs multiple uncoupled TCP flowsRetransmit timeouts with MPTCP (“linked”) vs uncoupled TCP flows
20 MPTCP Linked Increases in DCs Better fairness and less aggressive than uncoupled TCPImproves throughput in dense traffic in BCube (25%)
21 ? The bigger picture Resource Allocation Path Selection Routing MultipathTCPPath SelectionRoutingOSPF, VLANs, etc.Topology?FatTree, VL2, Bcube,multi-rooted tree
22 Multipath TCP can utilize topologies TCP can’t Requirement: a subset of hosts should be able to communicate at 10Gb/s1Gb/sShow multiple paths between serversSay that network is rearrangeably non blockingClos10Gb/s22
23 Multipath TCP can utilize topologies TCP can’t  ProblemToR switch failures wipe out tens of hostsRepair time is on the order of daysSolution: use two ToRs/rack, multi-home serversSingle path TCPSingle flows still get same max throughputWhich interface do I use?With Multipath TCPFlows double their maximum throughputPath selection automaticShow multiple paths between serversSay that network is rearrangeably non blockingClos23
24 SummaryData center networking offers many paths between end-hosts. Yet:Random Load Balancing does a poor job of utilizing themCentralized scheduling is laggy and has inherently limited knowledgeMultipath TCP naturally optimizes data center networks:Improves throughputImproves fairnessMore robust than centralized schedulingQuestion: what topologies does multipath TCP enable?
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